This invention relates generally to an apparatus and method to connect multiple optical fibers to a package, and more specifically to an apparatus and method to metallize optical fibers, reinforce metallized optical fibers, and hermetically seal the connection of metallized optical fibers to a package.
In many optical and electro-optical and optical packages and systems (e.g., computer systems, programmable electronic systems, telecommunication switching systems, control systems, and so forth) the reliable connection of multiple optical fibers to a package is desired, but difficult to achieve due to the fragile nature of the optical fibers and the water permeability of the polymer coating (e.g., urethane acrylate and equivalent polymers) surrounding each optical fiber. The migration of water into a package through the polymer coating surrounding each optical fiber has a detrimental effect on the operation and reliability of the components inside the package.
One solution for connecting one or more optical fibers to a package is to remove the polymer coatings surrounding each optical fiber and coat the bare optical fiber with a solderable metal, such as nickel or lead-tin solder. Then each optical fiber is soldered into an opening of a package with sufficient-solder to completely seal the optical fiber opening of the package. Prior art solutions are typically addressed to metal-coating each optical fiber on the very end of a bare optical fiber, one at a time.
However, this process introduces several new problems. One problem is that the optical fiber becomes very brittle and easy to break after the polymer coating is removed, since the polymer coating supplied mechanical support to the optical fiber. Another serious problem is created when the optical fiber is coated with a solderable metal, because the thermal shock of being coated with hot metal frequently degrades the optical and mechanical properties of the optical fiber. Furthermore, it is usually necessary to deposit multiple metal-coatings (creating multiple thermal shocks) on an optical fiber to achieve sufficient metal adhesion to the optical fiber. Additionally, it is extremely difficult to solder individual metal-coated optical fibers to package openings without breaking off the weakened metal-coated end of the optical fiber. Finally, it is also extremely difficult to solder multiple individual metal-coated optical fibers one-at-a-time, without the previously soldered optical fibers coming loose and shifting in position. Since the positioning of optical fibers is extremely critical to the optical coupling efficiency of the connection, even a shift between an optical fiber and a component exceeding 0.5 micron can be detrimental to the operation of an optical or electro-optical device.
FIG. 1 illustrates one approach for handling package connections in an electro-optical or optical system 100. Electro-optical system 100 shows an example of package 102 with ribbon cable 104 conventionally routed into the package 102 through opening or junction 106. FIG. 2A shows an example of a cross section of an individual fiber 200 from ribbon 104 in cross-section 2Axe2x80x942A from FIG. 1. As seen in a conventional assembly, individual fiber 202 may be typically surrounded by polymer coating 204 that is coated with a metal sleeve 206 and soldered into a wall at junction 106 of package 102. Polymer coating 204 may provide a path for the migration of water into package 102 and the eventual failure of components within electro-optical system 100. If coating 204 were removed from optical fiber 202, optical fiber 202 may become extremely brittle and easy to break during the process of soldering metal sleeve 206 to package 102.
Even if every opening is properly sealed by solder, the fragility of the optical fibers 202 near the soldered connections and the lack of mechanical reinforcement make it easy to break the optical fibers 202 when forces are imparted to the ribbon 104. The prior art metallization on the end of an optical fiber makes it difficult to mechanically clamp or reinforce the optical fiber near the soldering point. Mechanical clamping and reinforcement would be greatly facilitated by the extension of each optical fiber into a package. This would allow the optical fiber and package opening to be soldered some distance away from the end of the optical fiber. Then clamping and reinforcement could support the optical fiber on the outside of the package opening, as well as support the optical fiber on the inside of the package opening.
Furthermore, most optical and electro-optical systems may require several groups of optical fibers (e.g., bundled in ribbons of optical fibers) connected to one or more packages. The conventional method of connecting separate optical fibers to a package also has the disadvantage of requiring several package openings. Each package opening provides another point of entry for water into the package. Therefore, it would be preferable to minimize the number of package openings by connecting multiple optical fibers through one package opening to the components inside the package.
It would also be desirable to have the capability to selectively metallize multiple optical fibers in a bundled configuration along any segment of the bundle without breaking the optical fibers. The selective metallization would make it easier to reliably connect multiple optical fibers in a bundled (e.g., ribbon or cabled) configuration to a package using solder to seal the package opening to avoid moisture and gas migration into the package. It would also be desirable to provide an apparatus and method to reduce the stress on metallized optical fibers created by hermetically sealing the connection of metallized optical fibers to a package.
It is difficult to route optical fibers through a package opening for a component package. In such a case, metallized fibers may be used at the junction point where the fibers extend through the package wall to aid in sealing the package. However these fibers become very fragile and easy to break. Accordingly, apparatus and methods to metallize, reinforce, and hermetically seal multiple optical fibers are described herein.
A ribbon of optical fibers ranging from one to several dozen individual fibers may be placed into a fixture as described herein which preferably exposes only a select portion of the mid-span segment. The exposed portion may correspond to the geometry of the length of the ribbon segment to be stripped and metallized, as described below. The exposed segment of ribbon may be stripped of polymer coatings surrounding each of the individual fibers through a variety of methods, preferably by acid etching or alternatively by laser etching, etc. Then, a variety of metallic coatings may be deposited onto the bare segment of the optical fibers, preferably while the ribbon is still disposed within the fixture. The metallic coatings may comprise one to several layers, e.g., an adhesion layer, a solderable layer, and a protection layer.
Once metallized, the segment of optical fibers may then be positioned onto a metallic plate and soldered onto the plate for reinforcement of the metallized segment. Epoxy may additionally be deposited onto the fibers and plate to further affix the assembly. The plate and metallized segment may then be fed through a package opening. Once properly positioned within an opening, flux and additional solder may be melted around the gap defined between the plate and fiber assembly and the package opening. In addition to the solder, epoxy may also be applied over the solder to help protect the solder and additionally seal the package. This may result in a hermetic seal of the package preferably having a package leak rate less than about, e.g., 10xe2x88x929 AtmCC/sec (air) which is lower than an industry Mil-spec. standard of 10xe2x88x926 AtmCC/sec (air). The hermetic seal may also provide protection of the package interior from marine and salt environments.
Accordingly, part of the present invention may provide for the capability to selectively metallize multiple optical fibers in a ribbon configuration along any segment of the ribbon without breaking the optical fibers. It also may provide for the capability to reliably connect multiple optical fibers in a ribbon configuration to a package using solder to seal the package opening to avoid moisture and gas migration into the package. Also, stress on metallized optical fibers created by hermetically sealing the connection of metallized optical fibers to a package may be reduced.
Advantages of the invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.